I've never been one to size a tractor based on lot size. It's really about the tasks at hand to me. I have the CK25 on only 2.5 acres, and glad I didn't go smaller. So, I don't think the CK20S is too big. But, it is a lot more tractor than the MF. For loader work and snow removal, in most cases, the bigger heavier tractor would be best.
I do agree that you need to plan on a plow or blower for snow removal. I suggest to get a QA loader and a front mount blade. A rear blade will work too, and be cheaper. But you'll be constantly looking backward. That can get old if you have a lot of plowing to do. Same situation for the blower.
Whatever you choose, it's always a compromise in one way or the other. I don't like roll bars for mowing tasks. I have too man low hanging branches that would get in the roll bar, even if folded. And the CUTS are too heavy for mowing in the spring time. So, I have a separate machine for mowing. I keep looking for that one machine that can do it all, but haven't found it yet. Though I do like the TYM T273. It's about the closest I've seen. But TYM.... will they be here in 10 - 15 years?